[PATCH] [mc-coff] Forward Linker Option flags into the .drectve section

[Reid Kleckner]

Phab is down so here's the patch.

On Thu, Apr 25, 2013 at 12:43 PM, Reid Kleckner <rnk at google.com> wrote:
> On Wed, Apr 24, 2013 at 6:58 PM, Rafael Espíndola
> <rafael.espindola at gmail.com> wrote:
>>> +
>>> +  // Emit the linker options if present.
>>> +  if (LinkerOptions) {
>>
>> Please use an early return
>>
>> if (!LinkerOptions)
>>  return;
>
> Sure.
>
>>> +    const MCSection *Sec = getDrectveSection();
>>> +    Streamer.SwitchSection(Sec);
>>> +    for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
>>> +      MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
>>> +      for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
>>> +        MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
>>> +        Streamer.EmitBytes(" ");
>>> +        Streamer.EmitBytes(MDOption->getString());
>>>
>>
>> Is the format documented somewhere we could link to?
>
> The .drectve section format, or the module flags metadata format?
>
> The .drectve section, which we already use for dllexported symbols, is
> part of the PE-COFF spec:
> """
> A .drectve section consists of a string of text that can be encoded as ANSI or
> UTF8. If the UTF8 byte order marker (BOM, a three-byte prefix that consists of
> 0xEF, 0xBB, and 0xBF) is not present, the directive string is
> interpreted as ANSI.
> The directive string is a series of linker options that are separated
> by spaces. Each
> option contains a hyphen, the option name, and any appropriate attribute. If
> an option contains spaces, the option must be enclosed in quotes. The .drectve
> section must not have relocations or line numbers.
> """
>
> One thing that's a little vague is how quotes and backslashes should
> be escaped.  I'd guess it's the same escaping algorithm used for
> CreateProcess, since these are flags.
>
> Worth linking the doc here, or is the spec kind of an implicit reference?
>
> So far as I know, the metadata flags are only documented by
> implementation and mailing list discussion.  See Daniel's RFC about
> auto-linking:
> http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-January/058204.html
>
> Is it common to link the mailing list from the source code?
>
>>  Index: test/MC/COFF/linker-options.ll
>>> ===================================================================
>>> --- /dev/null
>>> +++ test/MC/COFF/linker-options.ll
>>> @@ -0,0 +1,28 @@
>>> +; RUN: llc -O0 -mtriple=i386-pc-win32 -filetype=obj -o - %s | llvm-readobj -s -sd | FileCheck %s
>>> +
>>
>> Please test the output of the assembly file. No need to use -filetype=obj.
>
> Sounds good.  For some reason I thought that wouldn't work with COFF,
> but it works fine.
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